To make feta sauce: In food processor mix yogurt, feta cheese, cucumber, one diced scallion and vinegar until smooth.,Add salt and pepper to taste.,Refrigerate while making burgers, or at least 15 minutes.,For burgers: Mix lamb, curry, remaining scallion and (generously)salt and pepper to taste.,______,In large skillet, heat olive oil on medium-high.,Cook patties until browned on outside and just cooked through(approx. 5 minutes each side).,Serve burgers on rolls topped with tomato slices and sauce.